The present invention relates to a method for joining extrusion members through friction stir welding so as to manufacture a structural body, for example a vehicle.
As disclosed in Japanese Patent Laid-Open Publication No. 9-309164 (EP 0797043A2), a friction stir welding is a technique in which a round shaft (called a rotary body) is rotated and inserted in the joint region of members to be joined, and the rotary body is moved along the junction line, thereby heating, mobilizing and plasticising the material, whereby a solid-phase welding of the members is achieved. The rotary body comprises a small-diameter portion to be inserted into the joint region, and a large-diameter portion to be positioned externally of the joint. The small-diameter portion and the large-diameter portion are coaxial, and the large-diameter side is coupled to a drive source. The boundary between the small-diameter portion and the large diameter portion is partially inserted into the joint region during welding. The joining of members performed by the friction stir welding method can be applied to both a butt joint and a lap joint.
Moreover, as shown in FIG. 7 of the above-mentioned publication, the joint region of the two members are provided with a protrusion extending toward the rotary body, which is to be used in the friction stir welding.
One example of the technique for manufacturing a railway car is disclosed in Japanese Patent Publication No. 6-45340, wherein the vehicle body of a railway car is manufactured by welding together extruded members made of aluminum alloy. The extruded member is equipped with a plural number of ribs provided on one surface of a face plate, which is placed on a frame with the surface not having the ribs facing downward, and welding is performed from the side having the ribs. The welding process is carried out so that a weld bead is formed on the back surface of the frame.
Since the surface without the ribs is used as the exterior surface of the vehicle body, the weld bead formed on the back surface can be cut off to form a smooth surface. Thereafter, a hairline finishing processe is performed on the exterior surface of the body. If necessary, a transparent coating is further applied to the surface. Or, in another example, the weld bead is cut off and putty is applied to the surface before the coating is applied.
Since the weld bead formed on the exterior surface of the vehicle body must be removed when the vehicle body is fabricated using a conventional welding process, the manufacturing process involves an increased number of steps. Moreover, when welding the vehicle body, the material is heated to a very high temperature, which causes deformation of the surfaces of the vehicle, and thereby deteriorates the appearance thereof. If the vehicle body is completed by a hairline finishing without coating the vehicle body, the weld bead formed at the welding portion degrades the appearance of the vehicle body. The weld bead varies in width and has a wavy appearance. This is why the weld bead degrades the exterior appearance of the body. Even if transparent coating is applied to the body after the hairline finishing, the appearance is not improved.
An object of the present invention is to manufacture a structural body, such as a vehicle body, having an attractive appearance using a friction stir welding method.
The foregoing object of the present invention is achieved by:
abutting the ends of the face plates of two members;
friction stir welding said ends of said face plates from only one side of said surface; and
performing buffing, blasting or coating on the opposite side of said surface from which said friction stir welding is performed, thereby finishing said surface to form the exterior surface of a structural body.